Electrochemical cells having thin planar anode assemblies have found particular applications in the medical field for use with heart pacemakers and other medical devices. General teachings concerning such cells may be found, for example, in U.S. Pat. No. 5,209,994 (hereinafter '994), assigned to the assignee of the present invention. The '994 cell includes a container of electrically conductive material which serves as a cathode current collector. The anode assembly of the cell includes a lithium element formed from two lithium halves which are pressed together with an anode current collector therebetween. The anode current collector extends to the exterior of the cell with use of an insulator which insulates a lead connected thereto from electrical contact with the container. The container is filled with a cathode material which is in operative contact with the exposed surfaces of the lithium element of the anode assembly. Similarly, the cathode material is in operative contact with the container. For enhanced performance of the cell, the opposed, major lateral surfaces (i.e., the "operative surfaces") of the lithium element may be coated with a film of electron donor material. More specifically, '994 describes this donor material as being a polymeric organic donor material such as poly (2-vinylpyridine). Such donor materials and application techniques for such materials are more fully described in U.S. Pat. No. 4,182,798.
In operation, a chemical reaction between the lithium element and the cathode material in the container causes excess electrons to flow into the current collector. A chemical reaction between the cathode material and the container causes the container to be positively charged. The resulting voltage differential can be used to power a device. To prevent the cell from short-circuiting, the anode current collector is electrically insulated from the cathodic container and from the cathode material which fills the container. As noted above, an insulator (i.e., a feedthrough) allows the anode current collector to extend to the exterior of the container without making electrical contact with the cathodic container. Additionally, the anode current collector is protected from contact with the cathode material by the seal formed by cohesion between the two lithium halves between which the collector is embedded.
In a conventional method for forming an anode assembly, two lithium pre-cut elements are positioned on opposite sides of an anode current collector. An insulated portion of the anode current collector which insulates the collector from the cathodic container is also typically positioned between the two lithium elements. The subassembly is then placed within two mold sections and is pressed together with a suitable force. The current collector and the insulator portion are sealed between the two lithium elements with a portion of the current collector (i.e., the lead) extending from the pressed together lithium elements for electrical connection of the electrochemical cell to a medical device.
Conventionally, the lithium halves are roughened, e.g., brushed, to enhance cohesion between the pre-cut lithium halves. Cohesion of the lithium halves sealing the anode current collector therein is necessary to prevent the cathode material from reaching the anode current collector and rendering the electrochemical cell inoperative. As such, techniques of enhancing such cohesion are needed.
In electrochemical cells, anode assemblies using lithium elements have been found to provide relatively small and efficient cells, particularly in conjunction with cathode materials, such as iodine or thionylchloride. However, costs associated with using pre-cut lithium halves to form such anode assemblies is of concern. Lithium has continuously been increasing in price as have labor costs associated with each pre-cut element. As such, there is a need for anode assembly configurations which at least hold the line on such costs.
Table 1 below lists U.S. Patents that describe electrochemical cells having thin plate anodes:
TABLE 1 U.S. Pat. No. Inventor(s) Issue Date 4,166,158 Mead, et al. Aug. 28, 1979 4,359,818 Zayatz Nov. 23, 1982 4,398,346 Underhill, et al. Aug. 16, 1983 4,401,736 Zayatz Aug. 30, 1983 4,421,833 Zayatz Dec. 20, 1983 4,601,962 Zayatz Jul. 22, 1986 4,812,376 Rudolph Mar. 14, 1989 4,824,744 Kuo et al. Apr. 25, 1989 5,209,994 Blattenberger et al. May 11, 1993
All patents listed in Table 1 above and elsewhere herein are hereby incorporated by reference in their respective entirety. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.